1. Field of the Invention
This invention relates to a method for "OR" optical switching in a waveguide particularly as activated by nonlinear optical signals and the optical switch so employed.
2. The Prior Art
Nonlinear optical processes have been the basis for many types of information processing. A component of these nonlinear optical processes is known as second harmonic generation (SHG). SHG has been observed in crystalline and oriented materials for over 30 years. The combination of second harmonic signals in a waveguide can be used as a switching mechanism. Numerous geometries have been predicted and tested.
Also in the prior art is U.S. Pat. No. 5,253,258 to Lawandy (1993) which discloses an optically encoded phased-matched SHG waveguide made of certain doped glasses and capable of self-frequency doubling of an input beam. However, there is no indication of employing two modes in the same waveguide for optical switching purposes.
The theory of frequency doubling of laser beams in certain channel waveguides is discussed at length in Frequency doubling in Ti:MgO:LiNbO.sub.3 channel waveguides by F. Laurell, J.Opt. Soc. Am. B/Vol. 5, No. 2 Feb. 1988, which Article is incorporated herein by reference.
Again while frequency doubling in certain waveguides is disclosed, there is no indication of employing two modes in a single waveguide for optical switching purposes.
Also one device used for the interference of optical signals is called a Mach Zender interferometer. In this device a laser beam that is propagating in a confined waveguide such as a fiber or channel waveguide on an integrated circuit, is split into two channels. One of the channels is modified by an external device that changes the propagation time down the channels. When the two beams are then recombined they destructively interfere if one of the beams has its phase shifted by 180 degrees related to the other beam. This is an electro-optic switch. However, laser beams in waveguides are very sensitive to temperature changes and a slight temperature difference between the channels can distort the phase shift between such beams and reduce the interference therebetween, once recombined, and cause inaccuracies in the above electro-optic switch.
Thus there is a need and market for an optical switch that reduces or obviates the above prior art shortcomings.
There has now been discovered a waveguide optic switch wherein a pair of laser beams are coupled into waveguide to generate interfering SHG beams and act as an on-off optical switch. As two modes of the same waveguide can be maintained at or near the same temperature, the optical switch of the invention has higher accuracy and reliability than previously available.